Measuring voltages while playing a 60 Hz sine wave. [resolved]

[Colonl_Charisma]

Quick update! I picked up a new RCA cable, and I took two new readings with a 60 Hz wave playing.

Old RCA cable measurements:
RCA left center pin = 1.487 V
RCA right center pin = 1.368 V

New RCA cable measurements:
RCA left center pin = 1.489 V
RCA right center pin = 1.488 V

 

[Paul Birkeland]

Time to junk that old cable.

 

[Colonl_Charisma]

Definitely haha. I'll listen for the rest of the day with the new cable, and I'll see if anything sounds off.

 

[Colonl_Charisma]

Hi, PB! I think you can mark this thread as resolved. I've been listening to my Crack for awhile now since switching out RCA cables, and I do not perceive any channel imbalance. What I was experiencing was pretty distinct.

Thanks for your help!

 

[Colonl_Charisma]

I'm back with some new measurements. Turns out my channel imbalance seems to still be present. My headphones sound balanced when just plugging them straight into my computer, but the right channel sounds quieter than my left channel when plugged into my Crack.

I followed the measurement instructions on this thread https://forum.bottlehead.com/index.php?topic=7788.15

My RCA jack measurements, middle lugs on potentiometer, and A2 and A7 were more or less equal. However, I seem to have a discrepancy when measuring AC voltage on terminals 1 and 5.

AC voltage with amp on and volume pot turned all the way up.
Terminal 1: 6.51
Terminal 5: 6.92

 

[Paul Birkeland]

That's half a dB, which is audible but not horrible.  What is the DCR of each headphone driver? 

You may find that tube rolling could yield more equal balance, or you could fit a balance control if you prefer.

 

[Colonl_Charisma]

I agree. It isn't as bad as what I was experiencing with the bad RCA cable, but I still notice it.

What does DCR mean? I am unfamiliar with the acronym haha.

 

[Paul Birkeland]

DC resistance.  You can use your meter to measure the resistance of each driver, though at 60Hz that measurement may not be so useful.

 

[Colonl_Charisma]

I can take the measurement now. Do I need to disassemble my HD600 to get to the driver?

 

[Paul Birkeland]

No, you can measure across the headphone plug.  The tip is L+, the ring is R+, and the sleeve is common.

 

[Colonl_Charisma]

Thanks for your help, PB! I am unable to post pictures (site not allowing it). Do I measure across the plugs that connect to the left and right sides of the HD600 while the headphone is plugged into the Crack with the 60hz sine wave playing?

 

[Paul Birkeland]

No, you unplug the headphones from the Crack and measure across the plug on the headphones.

 

[Colonl_Charisma]

My bad haha. Got those measurements for you!

L headphone DCR = 0.303 K ohms
R headphone DCR= 0.302 K ohms

 

[Paul Birkeland]

Yeah, I think you could try some different tube combinations to tighten up the channel balance.

 

[Colonl_Charisma]

Thanks, will do! The channel imbalance does seem less noticeable when using a 12AU7 tube compared to a 6SN7. I have a new problem now though haha. I opened up a new thread.

 

[Doc B]

That's half a dB, which is audible but not horrible

It's audible by a few with a lot of ear training, but not many.

 

[Paul Birkeland]

Doc brings up a good point, I'm not sure I would readily pick up on half a dB myself!

 

[Colonl_Charisma]

Right on! Doc B and Paul, it could easily be my mind playing tricks on me haha.

 

[Colonl_Charisma]

That's half a dB, which is audible but not horrible.  What is the DCR of each headphone driver? 

You may find that tube rolling could yield more equal balance, or you could fit a balance control if you prefer.

PB, you mentioned that I could try fitting a balance control. I am all about modding my Crack. How much space would be required to add one? I believe space to be my limiting factor.

 

[Paul Birkeland]

You'd need to fit the 100K linear version of the volume pot we supply, and you'd want it close to the volume pot itself.